Jar device

ABSTRACT

A jar for use in a downhole environment comprises a mandrel, a spline body, and a tool body, where the spline body provides a slideable engagement with the mandrel and anvil surfaces for absorbing the impact of the mandrel when the jar is fired, thereby providing a jar with no threaded connections in the impact path on a strong, one-piece mandrel.

FIELD OF THE INVENTION

The invention pertains to jars used in downhole environments to providean impact force, such as tools used to loosen stuck tool strings or forfishing.

BACKGROUND OF THE INVENTION

Jars, such as hydraulic jars, are used in downhole environments toprovide impact force. Such tools are useful when a fishing or drillingstring is stuck within a well bore and it is necessary to apply animpact force at the stuck location of the string to attempt to loosenit. Similarly, jars can be used in conjunction with fishing tools toprovide the fishing tool with sufficient force for operation, forexample, by providing an upward jarring force after the fishing tool hasengaged a stuck tool.

Jars may be constructed to provide an impact force in either the “up,”or “upward” (toward the surface) or “down,” or “downward” (away from thesurface) directions. Those of skill in the art will recognize that “up”and “down” are so defined because use of horizontal drilling techniquesmay result in situations in which “up” and “down” are not vertical.Similarly, as used herein, the “lower” portion of a tool or a partthereof is in the “downward” direction in respect to the “upper”portion. For maximum flexibility, ajar can be constructed to providebidirectional impact, that is, it can fire (provide impact blows) ineither the “up” or “down” directions at the choice of the operator onthe surface.

However, in some applications, particularly those using coiled tubing,the length of the tools used is of great importance. With coiled tubing,it is greatly desirable to have shorter tools, because multiple toolsmust often be assembled in combination at the surface, and the coiledtubing operation does not allow for successive assembly of tools as thestring is run into a pressured hole. Accordingly, it is sometimesdesirable to use ajar which fires in only one direction, because theneeded apparatus is shorter than one designed for bi-directional use.

Jars used in these applications operate by setting, or cocking, the jar,then applying an upward or downward force on the jar. These jarscomprise a mandrel, which moves relative to the tool body and whichbears the primary impact of the jar. Both the mandrel and the tool bodygenerally have anvil surfaces which form the contact surfaces where themandrel and the tool body meet. When the tool is released from the setposition, the mandrel and the tool body move relative to each other athigh speed, and the respective anvil surfaces strike with great force,thus producing the impact force of the jar. The relative direction oftravel of the mandrel to the tool body is determined by whether the jaris fired up or down.

Although the operation of such tools provides large impact forces whereneeded, the result is also a large amount of stress on the jar and itsvarious parts. Accordingly, repeated operations of these tools canresult in rapid wear and the need to replace or repair the jar. Becausereliability of operation is important, it is desirable that ajar bedesigned and constructed to accommodate repeated high stress. However,the tools are size-constrained by the standard sizes used for downholeoperations and the need for limiting the length of the tool, especiallyin conjunction with coiled tubing operations. In current jars, thesefactors have limited the ability of the tool to withstand repeatedoperations without the need for repair or replacement.

Accordingly, it is a goal of the invention to provide a jar that issubstantially shorter than current jars.

It is another goal of the invention to provide ajar with improvedcapability to withstand repeated operation cycles.

It is a further goal of the invention to provide a jar capable ofimproved impact force.

SUMMARY OF THE INVENTION

In the preferred embodiment, the invention comprises a hydraulic jarwith a mandrel, a spline body, and a hydraulic timing device. The jarcomprises an annular tool body, which is mechanically engaged with thespline body at the lower end of the jar. In the preferred embodiment,the spline body is threaded into the tool body. At its lower end, thespline body has a first anvil face which provides an impact surface foroperation of the jar when the tool is fired downward. At its upper end,the spline body has a second anvil face which provides an impact surfacefor operation of the jar when the tool is fired upward.

The mandrel comprises an annular body which is essentially cylindrical,and which extends through the spline body into the tool body. The lowerend section of the mandrel forms a first stop, the upper end of whichcomprises an anvil face for engaging the first anvil face of the splinebody. The upper end section of the mandrel forms a second stop, thelower end of which comprises an anvil face for engaging the second anvilface of the spline body. Thus, the mandrel body can slide up and downthrough the spline body, its travel limited only by the engagement ofthe first and second stops with the spline body.

In the preferred embodiment, the first stop of the mandrel is a formedportion of the mandrel body, which maximizes the strength of themandrel. Such maximum strength is desirable due to the force of theimpact when the first stop strikes the spline body when the jar isfired. However, the first stop may be made replaceable by making itdetachable from the remainder of the mandrel body, as by providing athreaded engagement. In such a case, it is desirable that the threads beradially as far as possible from the longitudinal axis of the jar toavoid undermining the strength of the jar.

The mandrel body comprises a plurality of longitudinal spline slots,which are preferably milled into the outer surface of the mandrel body.Similarly, the spline body comprises a plurality of longitudinal splineswhich are fittable into the spline slots in the mandrel body. In thepreferred embodiment, the spline body comprises a plurality oflongitudinal spline slots milled into the inner surface of the splinebody which do not extend to either end of the spline body, and splinesare set into the spline slots in the spline body. Additionally, in thepreferred embodiment, the spline body comprises a plurality of sections,preferably two longitudinal halves, into which the splines could be setand which can then be fitted around the mandrel body with the splines inslideable engagement with the spline slots of the mandrel body.Alternatively, the splines may be manufactured as part of the innersurface of the spline body.

The spline body and the mandrel are preferably of high strength ferrousor stainless steel. A variety of appropriate materials may be used.Those of skill in the art will recognize that some applications, such asdrilling applications, will impose higher torques on the device and willthus require stronger splines than will other applications.

In the preferred embodiment, the spline body can be assembled around themandrel prior to being threaded into the tool body, allowing for astronger, one-piece mandrel, as well as for ease of assembly and, ifnecessary, replacement of tool parts while simultaneously avoidinghaving any internal threaded structures in the impact path. Accordingly,this embodiment provides significant strength advantages andsimultaneously provides for ease of maintenance.

As those of skill in the art will recognize, it is possible to makevariations of the structure of this device without departing from thespirit of the invention. For example, the spline body could potentiallybe a cast piece, with the splines extending from the inner surfacewithout the need for milled spline slots or separately formed splines.

The spline body additionally preferably comprises a vent extending fromthe first anvil face of the spline body, through the spline body,providing fluid communication with the outside of the tool body and theannular space inside of the tool body. In the preferred embodiment, thesecond stop of the mandrel is formed to allow fluid communicationbetween the volumes above and below it within the tool body, that is, itdoes not form a seal with the tool body. Also in the preferredembodiment, an annular mandrel extension is threaded into and in sealingengagement with the second stop of the mandrel, and a floater provides aseal in the annular space above the second stop of the mandrel. Thefloater serves to equalize hydraulic pressure above and below it, sothat the hydraulic fluid within the hydraulic timer (discussed below) isnot contaminated by fluid from outside the tool, but the pressuresbetween the two fluids are automatically equalized.

In the preferred embodiment, the mandrel extension further extends intoan annular piston body, which is in mechanical engagement with the toolbody and serves as an extension thereof. The piston body preferablyprovides the housing for a hydraulic timing device, although othertiming devices, such as mechanical devices known to those of skill inthe art, could be used.

Prior art hydraulic timing devices sometimes utilize slidingmetal-to-metal seals which maintain a sealing engagement with the faceof an internal annular body, such as the piston body of the presentinvention, and a selective sealing engagement with the insidecircumference of an external annular body, such as the floater body orpressure body of the present invention. These devices are prepared forfiring by first positioning the seal in a sealing engagement with theexternal annular body by choosing a “vertical” position in which theinside circumference of the external annular body is small enough toengage the seal. The triggering device comprises a fluid channel, whichallows a small amount of hydraulic fluid to “leak” around the seal at aknown rate, thus allowing the seal to move at a regulated rate relativeto the external annular body when tensile or compressive force isapplied by the operator at the surface. The fluid channel may be anintegral part of the seal, such as a small channel in the seal material,or may otherwise be formed to provide a fluid pathway around the seal.The external annular body is formed with a transition region in whichits internal circumference increases beyond the maximum circumference ofthe seal, so that when the seal reaches this point, the hydraulic sealwill be rapidly released and the jar will “fire” in a sudden release ofapplied force.

In the preferred embodiment of the present invention, a slidingmetal-to-metal seal is in sealing engagement with the face of thefloater body or the pressure body, and in selective sealing engagementwith the outer circumference of the mandrel extension. In the preferredembodiment, the selective sealing engagement is accomplished by shapingthe mandrel extension so that its outer circumference varies, to providea region of sufficient circumference to engage the slidingmetal-to-metal seal, and a region of insufficient circumference toengage the seal. The device is set for firing by positioning it so thatthe seal is engaged with the outer circumference of the mandrelextension, then applying tensile or compressive force to the assembly. Afluid channel is provided to allow a controlled “leak” of hydraulicfluid around the seal, allowing the seal to slide in a controlledfashion to the point at which the outer circumference of the mandrelextension slopes inward and the seal is released. Those of skill in theart will recognize that the timing of the device can be altered, forexample by changing the size of the fluid channel or the length of thesection of the mandrel extension which provides sealing engagement withthe sliding seal.

Providing a sliding seal which springs inward greatly enhances thestrength of the device, because the floater body and the pressure bodyare of uniform thickness. In the prior art, the thickness of the floaterbody or pressure body had to decrease at the point at which the sealwould release, and remain at this decreased thickness for the length oftravel of the mandrel, so that the seal would not catastrophicallyre-engage with the inner circumference of the floater body or pressurebody. Maintaining a uniform thickness of the floater body or pressurebody prevents a “weak spot” in the wall of the floater body or pressurebody due to the inverse relationship of the hoop stress to the wallthickness.

If a bi-directional jar is desired, a second sliding seal may beincorporated into the hydraulic timing mechanism, preferably oriented inthe opposite longitudinal direction from the first sliding seal. Theoverall length of the mechanism can be limited by tapering the outercircumference of the mandrel extension at two locations, forming a“bulge” in the outer circumference which engages one of the two sealswhen tensile force is applied, and the other of the two seals whencompressive force is applied. Those of skill in the art will recognizethat it is mechanically possible to provide a bi-directional jar withmultiple seals which are oriented in the same longitudinal direction, solong as the fluid flow through the respective fluid channel for eachseal is appropriately directed. At some sacrifice of increased toollength, the jar can also be made bi-directional utilizing a single sealand a plurality of tapers on the outer circumference of the mandrelextension separated by sufficient distance to allow the jar to fullytravel in either direction.

Those of skill in the art will also recognize that the hydraulic timingdevice of the present invention may be used independently of the splinebody and mandrel combination described herein as part of the preferredembodiment of the device.

Those of skill in the art will further recognize that terms such as“mandrel extension,” “piston body,” and the like are for convenienceonly, and that a variety of single- or multi-part assemblies may beutilized in place of these parts without departing from the spirit ofthe invention.

As described above, the jar of the present invention can be used withgreater firing loads than similarly sized current jars.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a bi-directional jar in a firstfully “fired” position.

FIG. 1B is a cross-sectional view of a bi-directional jar in the“cocked”/middle position.

FIG. 1C is a cross-sectional view of a bi-directional jar in a secondfully “fired” position.

FIG. 2 is an enlarged cross-sectional view of the sliding seals on abidirectional jar.

FIG. 3A is an end view of the spline body

FIG. 3B is an enlarged cross-sectional view of the spline body

FIG. 4A is a cross-sectional view of the upper portion of an upward onlyjar.

FIG. 4B is a cross-sectional view of the lower portion of an upward onlyjar including a floater

FIG. 4C is a cross-sectional view of the lower portion of an upward onlyjar without a floater.

DETAILED DESCRIPTION

Referring to FIGS. 1A, 1B, and 1C, three positions of one embodiment ofajar of the present invention are shown. The depicted embodiment ismulti-directional jar, meaning that it can be fired in either an upwardor downward direction. Further, the preferred embodiment allowsconstruction of a short jar. FIG. 1A shows the jar in an fully “fired”condition, as it would be positioned after the jar was fired to exert anupward force on a stuck body. FIG. 1B shows the jar in a “cocked”position. FIG. 1C shows the jar in a fully “fired” condition, as itwould be positioned after firing the jar to exert a downward force.

Referring first to FIG. 1A, the jar 108 comprises a spline body 112, afloater body 118, which is threadably connected to the spline body 112via threading 146, a piston body 122 threadably connected to the floaterbody 118, and a pressure body 126 threadably connected to the pistonbody 122. The spline body 112 comprises a first anvil face 130 and asecond anvil face 132. Referring to FIGS. 3A and 3B, the spline body 312is shown in a larger view, and is shown to additionally comprise aplurality of spline slots 314 (only one such slot is visible due to thecross-sectional view) and vent ports 338. The vent ports 338 serve toallow fluid communication between the environment outside of the jar 108(of FIG. 1) and the interior of the jar 108. The spline body 312comprises two halves 340 and 342.

Referring again to FIG. 1A, the jar additionally comprises a mandrel 110with a plurality of mandrel spline slots 144 extending parallel to thelongitudinal axis of the mandrel 110. When the spline body 112 isassembled around the mandrel 110, splines (not shown) are held partiallyin the spline slots 314 (FIG. 3) of the spline body 112 and partially inthe mandrel spline slots 144, so that the mandrel 110 is rotationallylocked into position relative to the spline body 112, but slidableparallel to its longitudinal axis relative to the spline body 112. Inthe preferred embodiment, only two of such splines are used, but moremay be used without departing from the spirit of the invention.Assembling the spline body from two halves 340 and 342 (FIG. 3) allowsthe mandrel/spline combination to be easily assembled by enclosing thelong section 148 of the mandrel 110 within the two halves 340 and 342 ofthe spline body 112 before threading the spline body 112 into thefloater body 118.

The jar additionally comprises a mandrel extension 136 which ispreferably threadably connected to the mandrel 110. The mandrel 110 andthe mandrel extension 136 are annular cylindrical bodies.

The mandrel 110 comprises a first stop 140 which, if the mandrel 110 isslid fully into the remainder of the jar assembly, will contact againstthe first anvil face 130 of the spline body 112. Similarly, the mandrel110 comprises a second stop 142 which will arrest motion of the mandrel110 in the opposite direction by contacting the second anvil face 132 ofthe spline body 112. When the jar is “fired,” the first stop 140 orsecond stop 142 (depending on direction of travel) transfer the rapidrelative motion of the spline body 112 to ajarring force against themandrel 110, and thus into a fishing tool (not shown) or other toolattached to the mandrel 110.

The above-described combination of mandrel 110 and spline body 112allows the spline body 112 and the first stop 140 and second stop 142 ofthe mandrel 110 to be made with a relatively large thickness of solidmaterial around their respective annular cores, providing improvedstrength and durability over previously existing tools.

To allow equalization of pressure between the inside of the jar 108 andthe environment outside the jar 108, the vents 138 in the spline body112 allow fluid to enter or exit the jar 108 via the spline body 112 andaround the mandrel 110 via fluid channel 134 (FIG. 1C). An annularfloater 116 may be used to seal the fluid in the timing portions(discussed below) of the jar 108 from contaminants in external fluids.

Referring to FIG. 2, the timing portion of the jar 108 (FIG. 1) is shownin greater detail in its “cocked” position. The jar 108 is set in this“cocked” position, from which it may be fired either up or down. FIG. 2shows the end of the floater body 218, the piston body 222, and the endof the pressure body 226. The mandrel extension 237 extends through theannular space provided by the piston body 222. The mandrel extension 237has a circumferential bulge 236 over a portion of its length. The bulge236 is sufficiently large to allow selective engagement between themandrel extension 237 and first and second sliding seals 220 and 221.First sliding seal 220 provides a fluid seal between the mandrelextension 237 and the floater body 218, and second sliding seal 221provides a fluid seal between the mandrel extension 237 and the pressurebody 226. However, first and second sliding seals 220 and 221 alsocomprise first and second calibrated channels 234 and 235, respectively.Thus, first sliding seal 220 provides a substantial fluid seal betweenannular space 238 and the floater body bore 240, but allows fluid underpressure to travel at a controlled rate via first calibrated channel234. First calibrated channel 234 may by created by making a channel inthe first sliding seal 220, or by making a channel in the floater body218, with which the first sliding seal 220 is engaged. Similarly, secondsliding seal 221 provides a substantial fluid seal between annular space238 and the pressure body bore 242, but allows fluid under pressure totravel at a controlled rate via second calibrated channel 235. Secondcalibrated channel 235 may be created by making a channel in the secondsliding seal 221, or by making a channel in the pressure body 226, withwhich the second sliding seal 221 is engaged.

Referring again to FIG. 1A at the end 152 of mandrel extension 136, nut124 provides a seal to prevent pressure leakage from the jar mechanism.Pressure body 126 is connected to top sub 128, allowing the jar 108 tobe connected via top sub 128 to another device, such as a tool string orcoiled tubing for run-in to a downhole environment.

Referring again to FIG. 1 and the expanded view of FIG. 2, when the jar108 is positioned to apply force to some object, the jar 108 will thenbe “fired” to effect that force. For example, any of a variety offishing tools (not shown) which are well known in the art may beattached to the mandrel 110, and in turn be used to grab or connect to astuck object or a working tool. When it is desirable to fire the jar108, either upward or downward force is applied to the jar 108 via itsconnecting top sub 128. This force causes the piston body 222 to attemptto move relative to the mandrel extension 237, because mandrel extension237 and mandrel 110 are held in place by being connected to the stuckobject, thereby “cocking” the jar in preparation for firing it.

The amount of hydraulic pressure which builds up before the jar 108fires (and thus the amount of force transmitted to the mandrel 110 andthe stuck object) is determined by the force applied to the jar 108. Thetiming of the firing is controlled by the timing mechanism within thepiston body 222. If the jar is being fired “upward” (that is, movementof the piston body to the right side of FIG. 2 relative to the mandrelextension 237) the motion will be resisted by the near hydraulic lockcaused by the contact between first sliding seal 220 and the mandrelextension 237. However, some slow relative motion is allowed because thefirst calibrated channel 234 allows a small controlled flow of fluidaround first sliding seal 220. This slow relative motion between firstsliding seal 220 and the mandrel extension 237 will continue until thefirst sliding seal 220 reaches the first end 239 of bulge 236 in themandrel extension 237. At this point, first sliding seal 220 will nolonger maintain a seal, and the hydraulic pressure built up in the jar108 will release, with a resulting very rapid impact between the secondanvil face 132 of the spline body 112 and the second stop 142 of themandrel 110.

Conversely, if the jar is being fired “downward” (that is, movement ofthe piston body to the left side of FIG. 2 relative to the mandrelextension 237) the motion will be resisted by the near hydraulic lockcaused by the contact between second sliding seal 221 and the mandrelextension 237. However, some slow relative motion is allowed because thesecond calibrated channel 235 allows a small controlled flow of fluidaround second sliding seal 221. This slow relative motion between secondsliding seal 221 and the mandrel extension 237 will continue until thesecond sliding seal 221 reaches the second end 241 of bulge 236 in themandrel extension 237. At this point, second sliding seal 221 will nolonger maintain a seal, and the hydraulic pressure built up in the jar108 will release, with a resulting very rapid impact between the firstanvil face 130 of the spline body 112 and the first stop 140 of themandrel 110.

The timing of the jar 108, and the amount of stored pressure which isreleased on firing and the amount of force transferred to the stuckobject, is determined by the length of the bulge 236 and the rate offlow allowed through first or second calibrated channels 234 or 235,together with the amount of force applied to the jar 108 by theoperator.

Referring to FIG. 4, alternative embodiments of the jar 408 are shown.These embodiments of the jar 408 are somewhat more compact than those ofFIG. 1, because the jar 408 is configured to only be fired in the“upward” direction. Thus, there is a single sliding seal 420 in initialcontact with the bulge 438 of the mandrel extension 436. Thus, thisconfiguration eliminates the extra length required to allow the jar 408to fire in either direction.

The alternative embodiments of FIGS. 4B and 4C show the jar 408 with(FIG. 4B) and without (FIG. 4C) floater 416. If no floater is used, itis necessary to supply an O-ring seal 437 or other appropriate seal.Those of skill in the art will recognize that this alternativeembodiment can also be applied to the bi-directional jar of FIG. 1. Theabsence of the floater 416 allows for additional reduction in theoverall length of the jar 408.

The above examples are included for demonstration purposes only and notas limitations on the scope of the invention. Other variations in theconstruction of the invention may be made without departing from thespirit of the invention, and those of skill in the art will recognizethat these descriptions are provide by way of example only.

1. A jar comprising an annular tool body, comprising an interior, anannular spline body, comprising an exterior, wherein said spline body isin mechanical engagement with said annular tool body and wherein saidinterior of said annular tool body is in fluid communication with saidexterior of said annular spline body, and a mandrel, in slideable andessentially non-rotatable engagement with said spline body.
 2. The jarof claim 1, wherein said spline body additionally comprises a fluidchannel.
 3. The jar of claim 2, wherein fluid communication between saidinterior of said annular tool body and said exterior of said annularspline body occurs via said fluid channel.
 4. The jar of claim 1,wherein said annular spline body comprises an inner surface, and whereinsaid inner surface comprises a plurality of spline slots.
 5. The jar ofclaim 4, wherein said mandrel is held in engagement with said splinebody by splines in said spline slots.
 6. The jar of claim 1, whereinsaid mandrel comprises a plurality of spline troughs.
 7. The jar ofclaim 1, wherein said mandrel is held in engagement with said splinebody by splines in mechanical engagement with said spline body.
 8. Thejar of claim 6, wherein said mandrel is held in engagement with saidspline body by splines in slideable engagement with said spline troughs.9. The jar of claim 1, wherein said annular spline body comprises aninner surface, and wherein said inner surface comprises a plurality ofsplines.
 10. The jar of claim 9, wherein said mandrel is held inengagement with said spline body by said splines.
 11. The jar of claim1, wherein said spline body comprises a plurality of separable sections.12. The jar of claim 11, wherein said spline body additionally comprisesa fluid channel.
 13. The jar of claim 12, wherein fluid communicationbetween said interior of said annular tool body and said exterior ofsaid annular spline body occurs via said fluid channel.
 14. The jar ofclaim 13, wherein said annular spline body comprises an inner surface,and wherein said inner surface comprises a plurality of spline slots.15. The jar of claim 13, wherein said annular spline body comprises aninner surface, and wherein said inner surface comprises a plurality ofsplines.
 16. The jar of claim 1, wherein slideable motion of saidmandrel relative to said annular spline body is arrested in a firstlongitudinal direction by contact between said mandrel and said annularspline body.
 17. The jar of claim 1, wherein slideable motion of saidmandrel relative to said annular spline body is arrested in a secondlongitudinal direction by contact between said mandrel and said annularspline body.
 18. The jar of claim 14, wherein slideable motion of saidmandrel relative to said annular spline body is arrested in a firstlongitudinal direction by contact between said mandrel and said annularspline body.
 19. The jar of claim 14, wherein slideable motion of saidmandrel relative to said annular spline body is arrested in a secondlongitudinal direction by contact between said mandrel and said annularspline body.
 20. The jar of claim 14, wherein slideable motion of saidmandrel relative to said annular spline body is arrested in both a firstlongitudinal direction and a second longitudinal direction by contactbetween said mandrel and said annular spline body.